1. Field of the Invention
The present invention relates in general to automatic level controllers of a motor vehicle, and more particularly to the automatic level controllers of a type which carries out the vehicle height adjustment by using a fluid pressure, such as, air pressure and hydraulic pressure.
2. Description of the Prior Art
One of conventional automatic level controllers of a motor vehicle is described in Japanese Patent First Provisional Publication 5-77620. A control system of this level controller comprises a so-called jack-up judging means which issues a certain instruction signal when, under a vehicle body lowering control mode, the vehicle is judged to be jacked up, and a so-called jack-up promotion means which stops the vehicle body lowering control mode when receiving the certain instruction signal. That is, when the vehicle is standing with the level controller being under the body lowering control mode, the jack-up judging means carries out a judgment as to whether the vehicle is being jacked up or not by analyzing information signals issued from front and rear vehicle height sensors. More specifically, the jack-up judging means issues the instruction signal when the vehicle body is raised by a given degree from a reference level.
However, due to its inherent construction, the automatic level controller of the publication has failed to exhibit a satisfied performance.
That is, when, under the body lowering control mode at the standstill of the vehicle, the vehicle is jacked up by a suitable jack-up device 100 (see FIG. 4) and this jack-up handling is stopped before the vehicle body makes a sufficient rising from the reference level, the body lowering control mode is forced to continue. In this case, the pressurized air in air chambers of the level controller is fully discharged therefrom. Thus, when thereafter the jack-up device is handled to lower the vehicle body onto a road surface, it tends to occur that the vehicle stands on the road with its body remarkably and thus inelegantly lowered.
For ease of the following description, the handling for raising the vehicle body from a road surface by using a jack-up device will be referred to "jack-up handling", and the handling for lowering the raised vehicle body onto the road surface by using the jack-up device will be referred to "jack-down handling".